The alert that sends an email when a column value changes uses an Event Handler. This handler is created on the event list when the alert is created. If this event handler is missing or corrupted, our Support team may advise you to go to the Support tab of your Alert Plus web part. On the Support tab, click View to see the Event Handlers as shown in the screen shot below.
The Event Handlers section provides diagnostic information for Alert Plus event configuration. If you are working with Bamboo Support to resolve an Alert Plus issue, you may be directed to provide results from this section to Support during the troubleshooting process.